Party leader Nicola Sturgeon speaks at the Scottish National Party's conference in Aberdeen, Scotland

Party leader Nicola Sturgeon speaks at the Scottish National Party's conference in Aberdeen, Scotland, Britain March 18, 2017. REUTERS/Russell Cheyne

By Elisabeth O'Leary

ABERDEEN, Scotland (Reuters) - Refusal by Britain's prime minister to discuss an independence referendum would "shatter beyond repair" the United Kingdom's constitutional structure, Nicola Sturgeon told her Scottish National Party on Saturday.

Sturgeon, Scotland's First Minister, pledged to press on with plans to hold a new Scottish referendum as announced earlier this week, deepening a standoff with the UK government.

Party faithful cheered, clapped and leapt to their feet.

Sturgeon expects to get authorisation from the devolved Scottish parliament on Wednesday to seek the terms for a new secession vote, aiming for a date once the terms for Brexit are clear but before Britain leaves the EU.

"To stand in defiance of (Scottish parliamentary authorisation) would be for the prime minister to shatter beyond repair any notion of the UK as a respectful partnership of equals," Sturgeon said.

"Scotland's future will be in Scotland's hands."

Under the UK's constitutional arrangements, Britain's parliament needs to sign off on any legally binding vote in Scotland. Prime Minister Theresa May told Sturgeon this week that "now is not the time" for a new choice on independence as divorce talks between the world's fifth-largest economy and its erstwhile EU partners get under way. [L5N1GT4LN]

Although May did not deny a vote outright, Scottish nationalists predict her words could build support for secession because she could be seen as telling Scotland what to do.

"(May) has time to think again and I hope she does. If her concern is timing then - within reason - I am happy to have that discussion," Sturgeon said.

Britain is expected to trigger Article 50 of the EU's Lisbon Treaty within days and start the complex Brexit procedure.

Last June's vote to leave the EU has shaken the ties of the United Kingdom's four nations. England, the most populous, and Wales voted to leave while the Scots and Northern Irish wanted to keep their EU membership.

May's Conservatives, now the second biggest party in Scotland's parliament, called Sturgeon's speech disappointing and negative.

Scottish Conservative deputy leader Jack Carlaw accused her of "pursuing her own narrow agenda to the detriment and against the wishes of ordinary Scots".

The Scottish Labour Party said Sturgeon failed to mention poverty once, but mentioned independence 13 times.

In her speech, Sturgeon contrasted an image of an open and progressive Scotland against May's goal of limiting immigration across the UK.

"Scotland isn't full up. If you are as appalled as we are at the path this Westminster government is taking, come and join us," she said.

A ComRes opinion poll for the Sunday Mirror newspaper, published on Saturday but conducted before Sturgeon's speech, showed 59 percent of Britons think May should insist that a Scottish independence referendum should take place only after Britain leaves the EU.

"TIN EAR"

Scottish nationalists say the UK government has all but ignored their proposals for a bespoke deal for Scotland within Brexit.

"If (May) shows the same condescension and inflexibility, the same tin ear, to other EU countries as she has to Scotland then the Brexit process will hit the rocks," Sturgeon said.

She told Scottish television on Friday that she still has "options" if May refuses to acknowledge her mandate to call for a new vote, but declined to say what these were.

There has been talk at the conference of the possibility of a consultative referendum, a poll not authorised by the British parliament.

But "this is a step by step process. If we send an envelope to May and she returns it unopened, then we have the UK government not talking to the Scottish government," said a senior SNP source. "That is a constitutional crisis, or something very close to it."

Scottish voters rejected independence in 2014 by a 10 percentage point margin. But Sturgeon was elected last year on a manifesto which included the possibility of a new independence vote if there were a change in circumstances "such as Scotland being taken out of the EU against our will."

Speaking separately in Scotland, former British prime minister Gordon Brown - who still has sway with many Scots who want to keep ties to the UK - said Brexit had torn up the status quo and there was a need for new powers for the Scottish parliament.

"The third option, a patriotic Scottish way and free from the absolutism of the SNP and the do-nothing-ism of the (Conservatives) is now essential..." Brown, of the Labour Party, told a Festival Of Ideas in Kirkcaldy.

(This version of the story corrects the first name in para 13 to Jackson from Jack)